I use Volume Control Pro from the market to adjust and control my sound settings. The Widget gives me 3 presets, which I adjusted for normal, loud and off. I like the fact that I can set all six volume settings independently and instantly switch from one preset to another.
If the volume isn't loud enough for you on the highest volume settings and it seems as loud as other D3s, I am not sure what you can do....
Maybe it is time for a hearing test...